This is about interpretation of graphs.
Option C is correct.
From the graph, we can see the 2 lines representing function f(x) and function g(x).
Now for us to find the value of x in g(x) = k⋅f(x), we need get a mutual x-coordinate where we can easily read their respective y-coordinate values.
We see that the best point for that is where x = -3.
For f(x), when x = -3, y = 1
For g(x), when x = -3, y = -3
we can rewrite them as;
x = -3, f(-3) = 1 and x = -3, g(-3) = -3
Let us plug in the relevant values into g(x) = k⋅f(x) to get;
-3 = k(1)
Thus; k = -1/3